An RFID system includes an antenna of a reader/writer and an antenna of an RFID tag. Transmission and reception of a high-frequency signal of a UHF band is performed between the antenna of the reader/writer and the antenna of the RFID tag that are arranged so as to be adjacent to each other. A loop antenna including a loop conductor is used as the antenna of the reader/writer, and coil antennas including a plurality of laminated coil conductors are used as the antenna of an RFID tag. In addition, the conductor width of the loop conductor in the loop antenna is greater than the conductor widths of the coil conductors in the coil antennas.